Method and system for video equalization

ABSTRACT

Video equalization including performing equalization such that a sequence of images have dynamic range (optionally other characteristics) that is constant to a predetermined degree, where the input video includes high and standard dynamic range videos and images from both. Equalization is performed with a common anchor point (e.g., 20% gray level, or log mean of luminance) input video and the equalized video, and such that the images determined by the equalized video have at least substantially the same average luminance as images determined by the input video. Other aspects are systems (e.g., display systems and video delivery systems) configured to perform embodiments of the equalization method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/349,288, filed Apr. 2, 2014, which is a U.S. national stage ofInternational Application No. PCT/US2012/060230, filed Oct. 15, 2012,which claims priority to U.S. Provisional Application No. 61/549,433,filed Oct. 20, 2011, each of which is hereby incorporated by referencein its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to methods and systems for equalizing segments ofvideo of different types (e.g., high dynamic range (HDR) video andstandard dynamic range (SDR) video) such that a sequence of imagesdetermined by a sequence of the equalized segments has dynamic range(and optionally also at least one other characteristic, e.g., at leastone of color gamut, and white point) that is at least substantiallyconstant. Examples of systems configured to perform the equalization arevideo sources (e.g., broadcast installations) and display systems.

2. Background of the Invention

Throughout this disclosure including in the claims, the expressionperforming an operation “on” signals or data (e.g., filtering, scaling,or transforming the signals or data) is used in a broad sense to denoteperforming the operation directly on the signals or data, or onprocessed versions of the signals or data (e.g., on versions of thesignals that have undergone preliminary filtering prior to performanceof the operation thereon).

Throughout this disclosure including in the claims, the noun “display”and the expression “display system” are used as synonyms.

Throughout this disclosure including in the claims, the term “segment”of video (e.g., “segment” of a video program) denotes video data or avideo signal indicative of at least one frame (typically, a sequence ofconsecutive frames). A display system can display each frame as animage, and a sequence of the frames as a sequence of images, each saidimage having a dynamic range (a range of displayed pixel intensities).

Throughout this disclosure including in the claims, the expression thatan image is “determined by” video is used in a broad sense (whichcontemplates that the video may be an equalized or otherwise filteredversion of input video) to denote both an image determined by a frame ofthe video and an image determined by a corresponding frame of the inputvideo.

Throughout this disclosure, the expression “encoding” of video (e.g., avideo channel) denotes mapping a sequence of samples of the video to aset of values (“code values”) indicative of displayed intensities in arange from a minimum intensity (black level) to a maximum intensity,where each of the code values determines a displayed intensity of apixel (or a color component of a pixel, or a luminance or chroma valueof a pixel, or another pixel component) when the encoded video isdisplayed. For example, a video channel may be encoded in a linearmanner (so that the code values of the encoded video channel arelinearly related to displayed intensity values) or a nonlinear manner(so that the code values of the encoded video channel are nonlinearlyrelated to displayed intensity values).

Throughout this disclosure including in the claims, the expression“encoded video” denotes video determined by one or more channels of codevalues, each of the channels comprising a sequence of code values. Forexample, conventional Rec. 709 RGB video is encoded video comprisingthree channels of code values: a red channel comprising a sequence ofred (R) code values (red color component values), a green channelcomprising a sequence of green (G) code values (green color componentvalues), and a blue channel comprising a sequence of blue (B) codevalues (blue color component values). For another example, conventionalYCrCb video is encoded video comprising three channels of code values: aY channel comprising a sequence of luminance or luma code values (e.g.,luminance code values (Y), each of which is a weighted sum of linear R,G, and B color components, or luma code values (Y), each of which is aweighted sum of gamma-compressed R′, G′, and B′ color components), a Crchannel comprising a sequence of Cr (chroma) code values, and a Cbchannel comprising a sequence of Cb (chroma) code values.

Throughout this disclosure, the expression “peak white level” (or whitepoint) denotes the smallest code value (of a channel of encoded video)indicative of a pixel or pixel component (e.g., a color component of apixel, or a luminance or chroma value of a pixel) having maximumdisplayed intensity when the encoded video is displayed (assuming thatthe displayed pixels are determined by code values of the channel thatinclude the entire range of code values available for said channel, andcode values of any other channel that determine the displayed pixels areidentical for all the displayed pixels). To display the encoded videochannel, a video system may map to the maximum displayed intensity(e.g., clip or compress to the maximum displayed intensity) any codevalues of the channel that are larger than the peak white level.

Throughout this disclosure, the expression “black level” denotes thelargest code value (of a channel of encoded video) indicative of a pixelor pixel component (e.g., a color component of a pixel, or a luminanceor chroma value of a pixel) having minimum displayed intensity when theencoded video is displayed (assuming that the displayed pixels aredetermined by code values of the channel that include the entire rangeof code values available for said channel, and code values of any otherchannel that determine the displayed pixels are identical for all thedisplayed pixels). To display the encoded video channel, a video systemmay map (e.g., clip or compress), to the minimum displayed intensity,any code values of the channel that are smaller than the black level.

Throughout this disclosure, the expression “standard dynamic range” or“SDR” (or “low dynamic range” or “LDR”) channel denotes a channel ofencoded video (e.g., a channel of a video signal indicative of encodedvideo data) having bit depth equal to N (e.g., N=8, or 10, or 12), wherethe code values available for the channel are in a range from a blacklevel, X (referred to herein as a “standard black level”), to a peakwhite level, Z (referred to herein as a “standard white level”), where0≦X<Z≦2^(N)−1. It should be appreciated that the dynamic range of thecontent transmitted by a channel is often of greater importance than thedynamic range of the channel, and that either encoded video having afirst dynamic range (sometimes referred to as “low dynamic range video”or “standard dynamic range video” or “SDR video”) or encoded videohaving a dynamic range that is greater than the first dynamic range(sometimes referred to as “high dynamic range video” or “HDR video” withreference to the low dynamic range video) could be transmitted by an SDRchannel with the same bit precision but with different granularity.

Throughout this disclosure including in the claims, the expression“standard dynamic range” (or “SDR” or “low dynamic range” or “LDR”)video system denotes a system configured to display, in response to SDRvideo having at least one SDR channel, an image sequence (or image)whose luminance has a dynamic range (sometimes referred to herein as astandard dynamic range). Herein, the term “luminance” (of an image orimage sequence) is used in a broad sense to denote luminance of theimage or image sequence, or intensity (or brightness) of the achromaticportion of the image or image sequence, or intensity (or brightness) ofthe image or image sequence. It should be appreciated that the peakbrightness of a physical display can change depending on its whitepoint.

Throughout this disclosure, the expression “high dynamic range” (or“HDR”) channel, used with reference to an SDR channel (or SDR videowhose channels are all SDR channels), denotes a channel of encoded video(e.g., a channel of a video signal indicative of encoded video data)having dynamic range greater than that of the SDR channel (or than thatof each channel of the SDR video). For example, the HDR channel may havebit depth greater than N (where each SDR channel has bit depth equal toN) or the code values available for the HDR channel may be in a rangefrom a minimum value, Min, to a maximum value, Max, where0≦Min<X<Z<Max≦2^(N)−1, where X is a standard black level, and Z is astandard white level (and where the code values available for each SDRchannel are in the range from X to Z.

An example of HDR video is “visual dynamic range” (VDR) video, which isvideo data (or a video signal) capable of being displayed by a displaysystem with the full dynamic range perceivable by a human viewer undernormal display viewing conditions. One type of VDR video is described inPCT International Application PCT/US2010/022700, by Dolby LaboratoriesLicensing Corporation (published as PCT International ApplicationPublication No. WO 2010/104624 A2).

In one conventional SDR display system which operates with 8 bit YCbCrvideo signals, with the code value 235 considered the maximum level (sothat the code values in the range from 236-254 are not used to displayimages), code value 16 (cast into absolute units for a referencedisplay) represents about 0.01 cd/m² (0.01 candelas per square meter,where the unit “candelas per square meter” is sometimes referred to as“nits) and code value 235 represents about 100 cd/m². The maximumdynamic range of the SDR content of such a system is thus 0 through 100nits. The maximum dynamic range of the SDR content of some otherconventional SDR display systems is 0 through 500 nits. It should beappreciated that the present invention is applicable to encoded video ofany bit depth, although some systems and methods are described withreference to encoded video of a specific bit depth (for clarity).

A video broadcast system may broadcast both SDR and HDR video content,for example, a video program comprising a sequence of HDR video segments(e.g., segments of a movie or TV program) time-division multiplexed withSDR video segments (e.g., commercials).

FIG. 1, which depicts a conventional video broadcast system, includes asimplified block diagram of national broadcaster installation 1 (e.g.,NBC National) and a simplified block diagram of regional broadcasterinstallation 3 (e.g., Seattle NBC). Installation 1 (sometimes referredto herein as subsystem 1) is configured to broadcast a video outputstream to regional installation 3 (sometimes referred to herein assubsystem 3) via delivery subsystem 2. Subsystem 2 may implement astandard (e.g., cable or satellite) transmission path. The video outputstream may be stored by subsystem 2 (e.g., in the form of a DVD or Bluray disc), or transmitted by subsystem 2 (which may implement atransmission link or network), or may be both stored and transmitted bysubsystem 2.

In subsystem 1, switcher 5 is coupled to receive video input streams 4A,4B, and 4C (which may be stored on suitable storage media). Inputstreams 4A, 4B, and 4C are typically of different types in the sensethat at least one video characteristic of each (e.g., at least one ofcolor gamut, dynamic range, and white point) differs from at least onecharacteristic of a least one other one of said input streams. Each ofstreams 4A, 4B, and 4C is an encoded video stream in the sense that itcomprises a sequence of code words indicative of input video. Switcher 5(sometimes referred to as “to the air” switcher 5) is configured toselect which of the input streams is to be broadcast, and totime-division multiplex the selected content (or insertion spots orother markers for content) into the combined stream to be output todelivery subsystem 2. Switcher 5 typically can insert into the combinedstream either insertion spots for commercials (downstream triggerpoints) or commercials themselves. Within digital modulator 7 ofsubsystem 1, the combined (time-division multiplexed) stream iscompressed (e.g., via MPEG-2 encoding) and typically also scrambled, andmodulated for delivery over a physical network. For simplicity,management software is not shown in FIG. 1, but installation 1 wouldtypically employ such software to implement scheduling, tracking ofcommercials, and billing.

In demodulator 9 of regional broadcasting installation (subsystem) 3, adelivered signal received from subsystem 2 is demodulated, to recover anencoded video stream (e.g., an MPEG-2 encoded video stream of the typegenerated in modulator 7 of installation 1). In splicing subsystem 6,local commercials, live sports casts, and news shows (which aretypically MPEG encoded by local encoder 8) are spliced (time-divisionmultiplexed), as required, into the stream recovered in demodulator 9.

Throughout the delivery chain implemented by the FIG. 1 system, thereare several sources of content that can be placed into distribution,including the sources coupled to the inputs of switcher 5 and sourcescoupled to the inputs of encoder 8 (or splicer 6). Video from eachsource can have a different dynamic range, gamut (color gamut), or evenwhite point. Thus consumer who views a display generated in response tothe broadcast output (i.e., a time-division multiplexed sequence ofvideo segments from different ones of the sources) may noticeundesirable fluctuations in brightness (and/or color gamut and/or colortemperature and/or at least one other parameter) during transitionsbetween the segments (e.g., during transitions between commercial andnon-commercial content). This problem can be especially severe when thebroadcast video is a sequence of HDR (e.g., VDR) video segments and SDRvideo segments.

Thus, implementation of a visual dynamic range (VDR) or other HDR videodelivery pipeline will encounter obstacles due to the need to delivervideo content from multiple sources through the same pipeline, where thecontent from each source is, in general, of a different type (e.g., hasdifferent dynamic range, color gamut, and/or white point).

For example, during capture of a sporting event, a mixture of HD and SDcameras could be employed to generate both HDR (e.g., VDR) and SDR videocontent to be delivered. If the content is left unprocessed, the imagedisplayed (in response to the content delivered via the pipeline) couldhave large steps in luminance levels or different gamuts. For example,the bitstream sent down the pipeline might include SDR content capturedwith SD cameras which has half the brightness and wash out (smallergamut and white point) than HDR studio content captured with HD cameras.Consider another example in which an HDR television show to be deliveredvia a pipeline has SDR commercial content inserted into the streamdelivered over the pipeline. A consumer who views the pipeline outputmay notice fluctuations in brightness during transitions betweencommercial and non-commercial content.

Other video delivery pipelines may need to deliver video source content(e.g., commercials, TV shows, and movies) having different dynamicranges, gamuts and/or white points, via broadcast, or OTT delivery(“over the top” delivery by internet-based technology) or VOD (video ondemand) delivery. The inventor has recognized that, in this context,there is a need to be able to adjust all the content intelligently toensure a consistent viewing experience. For example, there may be a needto adjust the display of delivered content at the terminating displaywhen content switches between a VDR movie (or TV show) and commercials.The commercials may have been introduced into the delivered stream atthe last moment and this introduction could result in a mixture of SDRand HDR formats within the streamed content. The overall brightness ofthe displayed content could have significant jumps and not be pleasingto the viewer. During video broadcast (or OTT video delivery or VODdelivery), commercial vendors may not wish to store both an HDR (e.g.,VDR) and SDR version of a commercial to be inserted in the stream to bedelivered.

Some embodiments of the invention are methods (implemented at any of atdifferent stages in a video delivery pipeline) for equalizing dynamicrange of video content (e.g., captured camera data), typically byimplementing an automated video equalization algorithm Videoequalization in accordance with the invention can be implemented atvarious points in a delivery pipeline, e.g., at distribution (e.g., in abroadcast installation, or an OTT or VOD delivery installation), or in adisplay system which displays the delivered content. The inventor hasrecognized that managing video equalization at the display system canprovide the benefit of ensuring a constant viewing experience whilechannel surfing, switching video sources, and proper adjustments toon-screen displays between the modes.

The inventor has also recognized that in order to preserve artisticintent, the inventive video equalization should be implemented with acommon anchor point for the input video and equalized video, and so thatthe displayed image(s) determined by the equalized video have at leastsubstantially the same average luminance as the displayed image(s)determined by the input video. In contrast, simple mapping of codevalues of input video (having one dynamic range) to code values ofequalized video (having a different dynamic range) without a commonanchor point would typically destroy the artistic intent of the inputvideo's originator (e.g., it could cause the displayed images determinedby the equalized video to have much different aesthetic characteristicsthan those determined by the input video).

BRIEF DESCRIPTION OF THE INVENTION

In a first class of embodiments, the invention is a method including astep of performing equalization on input video to generate equalizedvideo, such that a sequence of images determined by the equalized videohave dynamic range (and optionally also at least one othercharacteristic, e.g., at least one of color gamut and white point) thatis constant to a predetermined degree (e.g., at least substantiallyconstant), where the input video includes high dynamic range (HDR) videoand standard dynamic range (SDR) video, and the images include at leastone image determined by the high dynamic range video and at least oneimage determined by the standard dynamic range video. The equalizationis performed with a common anchor point (e.g., a gray level at leastsubstantially equal to a 20% gray level, or another predetermined graylevel, or the log mean, or average, or geometric mean, or log of thegeometric mean of luminance) for the input video and the equalizedvideo, and such that the images determined by the equalized video haveat least substantially the same average luminance as images determinedby the input video. In some embodiments in the first class, theequalization includes a step of mapping code values of the SDR video tocode values in a subrange of a full range of code values employed toencode the HDR video, such that the mapping expands the SDR video'sdynamic range (or otherwise aligns the SDR video's dynamic range withthat of the HDR video), while maintaining average luminance of the SDRvideo at least substantially unchanged and windowing the equalized SDRvideo and the equalized HDR video to a common anchor point (e.g., bymapping the SDR video's 20% gray level to the HDR video's 20% graylevel, or mapping the log mean (or average, or geometric mean, or log ofthe geometric mean) of the SDR video's luminance to the log mean (oraverage, or geometric mean, or log of the geometric mean) of the HDRvideo's luminance).

In some embodiments in the first class (typically implemented in abroadcast installation or other video delivery installation), the methodincludes the steps of performing the equalization on segments ofdifferent streams of the input video to generate equalized videosegments, and combining (e.g., time-division multiplexing) the equalizedvideo segments into a combined video stream, wherein the equalizationadjusts video of at least one of the segments of the input video suchthat images determined by the combined video stream have a dynamic range(and optionally also at least one other characteristic) that is at leastsubstantially constant although the images are determined by frames,that do not have at least substantially constant dynamic range, of asequence of different ones of the streams of the input video.

In some embodiments in the first class (typically implemented by adisplay system), the method includes a step of performing videoequalization on segments of a video stream (e.g., a decoded version ofan encoded video stream received from a video delivery system) togenerate a sequence of equalized video segments, wherein the videoequalization adjusts video of at least one of the segments such that asequence of images determined by the sequence of equalized videosegments has dynamic range (and optionally also at least one othercharacteristic) that is at least substantially constant, although imagesdetermined by the segments of the video stream do not have at leastsubstantially constant dynamic range. Typically, these embodiments ofthe method also include a step of determining the video equalization tobe performed on each of the segments by analyzing the video stream, ordetermining (from metadata provided with the video stream) the videoequalization to be performed on each of the segments.

In another class of embodiments, the invention is a system configured toperform any embodiment of the inventive equalization method. In somesuch embodiments, the invention is a display system including anequalization stage configured to perform any embodiment of the inventiveequalization method on input video to generate equalized video, and asubsystem coupled and configured to display images in response to theequalized video. In other embodiments, the inventive system is a videodelivery system (e.g., a broadcast system). In some such embodiments,the video delivery system is or includes at least one of an upstreamstage (e.g., national broadcast installation) configured to performvideo equalization in accordance with the invention, and a downstreamstage (e.g., regional broadcast installation) configured to performvideo equalization in accordance with the invention.

In some embodiments, the invention is a processor configured to performany embodiment of the inventive equalization method. In otherembodiments, the invention is a system including such a processor and asubsystem for providing (e.g., generating) input video to be equalizedin accordance with the invention, and optionally also one or both of adelivery subsystem configured to store and/or transmit an encodedrepresentation of equalized video generated in accordance with theinvention, and a display subsystem for displaying equalized videogenerated in accordance with the invention. Embodiments of the inventiveprocessor are (or include) a general or special purpose processor (e.g.,a digital signal processor or microprocessor implemented as anintegrated circuit (chip) or chip set) which is programmed with software(or firmware) and/or otherwise configured to perform an embodiment ofthe inventive method. Another aspect of the invention is a computerreadable medium (e.g., a disc) which stores code for programming aprocessor to implement any embodiment of the inventive method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional broadcast system.

FIG. 2 is a block diagram of an embodiment of the inventive system.

FIG. 3 is a diagram of a code value mapping performed in accordance withan embodiment of the inventive method.

FIG. 4 is a block diagram of another embodiment of the inventivebroadcast system.

FIG. 5 is a block diagram of a system, including display system 50,wherein display system 50 implements an embodiment of the inventivevideo equalizer.

FIG. 6 is a block diagram of a display system (60) which implementsanother embodiment of the inventive video equalizer.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the inventive video delivery system will be describedwith reference to FIGS. 2 and 4, and embodiments of the inventivedisplay system will be described with reference to FIGS. 5 and 6.

The system of FIG. 2 implements a broadcast pipeline similar to thatimplemented by the conventional FIG. 1 system, except that it ismodified in accordance with an embodiment of the invention to applyequalization to input video from multiple sources (e.g., streams 4A, 4B,and 4C). The input video includes at least one HDR video stream (e.g., aVDR video stream) from at least one of the sources, and at least one SDRvideo stream from at least one of the sources. The FIG. 2 system isidentical to that of FIG. 1 (and elements of FIG. 2 that correspond toelements of FIG. 1 are identically numbered in both figures) except inthat national broadcaster installation 31 of FIG. 2 differs frominstallation 1 of FIG. 1 by including video equalization subsystem 10coupled between its video sources and switcher 5, and in that regionalbroadcaster installation 33 of FIG. 2 differs from installation 3 ofFIG. 1 by including decoder 11, switcher 19, video equalizationsubsystem 20, and encoder 12 (connected as shown) in place of localencoder 8 and splicer 6. In demodulator 9 of regional broadcastinginstallation 33, the received signal is demodulated to recover anencoded video stream (typically an MPEG-2 encoded stream), and theencoded stream is decoded in decoder 11 (typically implemented as anMPEG-2 decoder). Switcher 19 (which can be identical to “to the airswitcher” 5 of installation 31) is configured to select what content ismultiplexed into the stream to be broadcast by installation 33. Thevideo content multiplexed by switcher 19 includes at least one stream ofHDR (e.g., VDR) video and at least one stream of SDR video. Switcher 19typically time-division multiplexes local commercials, live sportscasts, and news shows (which are typically MPEG encoded by local encoder8) with the decoded stream output from decoder 11. Video equalizationsubsystem 20 performs equalization on the time-divisional multiplexedstream output from switcher 19 in a manner to be described below, andencoder 12 (typically implemented as an MPEG-2 encoder) encodes theoutput of equalization subsystem 20, typically by performing the inverseof the decoding performed by decoder 11.

Video equalizer 10 (in national broadcaster installation 31 of FIG. 2)is configured to equalize the streams video content asserted to itsinputs to generate streams of equalized video, and switcher 5 isconfigured to combine (time-division multiplex) selected segments of thestreams of equalized video to generate a combined stream, such that thedynamic range of the combined stream output from switcher 5 (and thedynamic range of the compressed (e.g., MPEG-2 encoded) and modulatedversion of the combined stream output from installation 31) is constantto a predetermined degree (e.g., at least substantially constant)although its content is from a sequence of different input video streams(including both HDR and SDR video streams). Optionally also at least oneother characteristic (e.g., at least one of color gamut and white point)of the combined stream output from switcher 5 (and the compressed andmodulated version of the combined stream output from installation 31) isalso constant to a predetermined degree (e.g., at least substantiallyconstant) although its content is from a sequence of different inputvideo streams (including both HDR and SDR video streams). In someoperating modes, switcher 5 inserts, into the combined stream, insertionspots for commercials (downstream trigger points) rather thancommercials themselves (i.e., insertion spots for commercials, ratherthan commercials determined by equalized video output from equalizer 10)Similarly, video equalizer 20 (in regional broadcaster installation 33of FIG. 2) is configured to adjust the video content at its inputs sothat the dynamic range of the combined stream output from equalizer 20(and the encoded version of this combined stream that is output frominstallation 33) and optionally also at least one other characteristicof the combined stream (e.g., at least one of its color gamut and whitepoint) is constant to a predetermined degree (e.g., at leastsubstantially constant) although its content is from a sequence ofdifferent input video streams (including both HDR and SDR videostreams). The video equalization (implemented by equalizer 10 or 20, orby elements 55 and 57 of the FIG. 5 system or elements 65 and 67 of theFIG. 6 system to be described below) is performed with a common anchorpoint (e.g., a gray level at least substantially equal to a 20% graylevel, or another predetermined gray level, or the log mean, or average,or geometric mean, or log of the geometric mean of luminance) for theinput video and equalized video, and such that displayed imagesdetermined by the equalized video have at least substantially the sameaverage luminance as corresponding displayed images determined by theinput video.

In variations on the FIG. 2 system, one but not both, of an upstreamstage (e.g., national broadcast installation) and a downstream stage(e.g., regional broadcast installation) of a video delivery (e.g.,broadcast) system, is configured to perform video equalization inaccordance with the invention. For example, installation 31 of FIG. 2 isreplaced by installation 1 of FIG. 1, or installation 33 of FIG. 2 isreplaced by installation 3 of FIG. 1. In other embodiments of theinvention (e.g., the embodiments to be described with reference to FIGS.5 and 6), a display system, to which video has been delivered by a videodelivery system, is configured to perform video equalization on thedelivered video in accordance with the invention.

HDR content (e.g., one of video streams 4A, 4B, and 4C) to be delivered(with SDR video content) by the FIG. 2 system may have a dynamic rangeof 0 through 10K nits, while the dynamic range of SDR content to bedelivered (e.g., legacy content determined by another one of streams 4A,4B, and 4C) is 0 through 100 (or 500) nits, where “nit” denotes candelasper square meter. In a typical implementation of FIG. 2, each of the SDRand HDR video streams asserted to the inputs of equalizer 10 is encodedas a sequence of code words, each of the code words having value in therange from 0 through 1, where the code word “1” denotes maximumdisplayed intensity (e.g., 100, 500, or 10K nits, depending on thespecific type of the video content). The bit depths of the SDR and HDRvideo streams can be identical or different. The input video indicatedon the left side of FIG. 3 is encoded in such a manner.

In a typical implementation of FIG. 2, SDR video content (e.g., one ofstreams 4A, 4B, and 4C, or one of the streams input to switcher 19) tobe delivered (with HDR video content) is equalized (e.g., in equalizer10 or 20) by mapping its code values to code values in a subrange of thefull range of the HDR content's encoding scheme, such that the mappingexpands the dynamic range of the SDR content while keeping the mean ofthe equalized SDR content's luminance at least substantially equal tothat of the original SDR content. Preferably also, the mapping windowsthe equalized SDR content and the equalized HDR content to a commonanchor point (e.g., by mapping the SDR content's 20% gray level to the20% gray level of the HDR content, or mapping the log mean (or average,or geometric mean, or log of the geometric mean) of the SDR content tothe log mean (or average, or geometric mean, or log of the geometricmean) of the HDR content).

For example, consider the case diagrammed in FIG. 3 in which the fullrange of code values output from the video equalizer (e.g., equalizer 10or 20) is the range from 0 through 1, the full range of code values of300 nit input SDR content (input to the equalizer) is also the rangefrom 0 through 1, and the full range of code values of 10,000 nit HDRcontent (input to the equalizer) is also the range from 0 through 1.Thus, the FIG. 3 example assumes that the full signaling range for alltypes of video content input to (or output from) the video equalizer isfrom 0 through 1, in the sense that each video stream input to theequalizer and each video stream output from the equalizer is encoded asa sequence of code words, each of the code words having value in therange from 0 through 1. With this assumption, during one type of videoequalization in accordance with the invention, the code values of inputSDR video (e.g., 300 nit SDR video, as indicated in FIG. 3) are mapped(in a “first stage” of mapping) to values in a subrange from 0 through Tof the full range of the HDR encoding scheme, where T is substantiallyless than 1. In the FIG. 3 example (and typical embodiments of theinventive method), the value T is the HDR video code word valueindicating a pixel (or color component) of HDR content having luminanceequal to the maximum luminance (300 nits in the FIG. 3 example) of theSDR video to be time-division multiplexed with the HDR content. Themapped SDR code values (resulting from the first stage of mapping) arethen further mapped to a wider subrange of the full range of the HDRencoding scheme, such that the further mapping (a “second stage” ofmapping) expands the dynamic range of the SDR content while keeping themean of the mapped (equalized) SDR content's luminance at leastsubstantially equal (equal or substantially equal) to that of theoriginal SDR content. However, the code values of input HDR video passthrough the equalizer unchanged. In embodiments of this type, the videoequalization does not change the input HDR content.

Preferably, the second stage of mapping also windows the equalized SDRcontent and the equalized HDR content to a common anchor point in thesense that it maps one predetermined code value (of the code valuesresulting from the first stage of mapping) to the same (or substantiallythe same) predetermined code value of the code values of the HDRencoding scheme. For example, the predetermined code value may be the20% gray level of the HDR content, so that the second stage of mappingmaps the code value (of the code values resulting from the first stageof mapping) indicative of 20% gray level to the code value (of theequalized SDR code values resulting from the second stage of mapping)indicative of 20% gray level). For another example, the predeterminedcode value may be the code value (of the HDR content) which is the logmean of the luminance of the SDR code values being equalized, so thatthe second stage of mapping maps the code value (of the code valuesresulting from the first stage of mapping) which is the log mean of theluminance of the SDR code values being equalized, to the code value (ofthe equalized SDR code values resulting from the second stage ofmapping) which is the log mean of the luminance of the SDR code valuesbeing equalized. Such mapping (which expands the dynamic range of theSDR content while keeping the mean of the equalized SDR content'sluminance at least substantially equal to that of the original SDRcontent and windowing the equalized SDR content and equalized HDRcontent to a common anchor point) is performed in order to preserve theartistic intent of the SDR input video's originator (in an effort tocause displayed images determined by the equalized SDR video to have atleast substantially the same aesthetic characteristics as thosedetermined by the original, unequalized input SDR video).

In some embodiments of the inventive equalization, the expansion of thedynamic range (of input SDR video) which is implemented by theabove-described mapping of input SDR video code values (which mappingalso keeps the mean of the equalized SDR content's luminance (e.g.,intensity or brightness) at least substantially equal to that of theinput SDR content) is accomplished by histogram encoding (e.g., asdescribed in U.S. Provisional Patent Application No. 61/453,922, filedMar. 17, 2011 by Anders Ballestad and Gerwin Damberg, or in U.S.Provisional Patent Application No. 61/474,733, filed Apr. 12, 2011 byAnders Ballestad and Gerwin Damberg, or U.S. Provisional PatentApplication No. 61/506,903, filed Jul. 12, 2011 by Anders Ballestad andGerwin Damberg, all assigned to the assignee of the present application.The full disclosure of each of these provisional applications is herebyincorporated by reference into the present application. Alternatively,the expansion of the dynamic range (of the input SDR video beingequalized) is implemented in another manner, e.g., by light sourcedetection expansion (e.g., as described in PCT International ApplicationPublication No. WO 2010/132237 A1, published on Nov. 18, 2010, filed byDolby Laboratories Licensing Corporation, and assigned to the assigneeof the present application), or by expanding only the upper luminanceband blindly (straight line expansion). The full disclosure of the PCTInternational Application referenced in the previous sentence is herebyincorporated by reference into the present application. As mentioned,the mapping which implements the dynamic range expansion preferably alsowindows the equalized SDR content and the equalized HDR content to acommon anchor point (e.g., by mapping the SDR content's 20% gray levelto the 20% gray level of the HDR content, or mapping the log mean of theSDR content to the log mean of the HDR content).

When SDR input video and HDR input video (of the type equalized intypical embodiments of the invention) is encoded as a sequence of codewords, each of the code words having value in the range from 0 through1, and such encoded video is conventionally employed (withoutequalization in accordance with the invention) to display images (asequence of SDR and HDR images), the displayed images can fluctuatesignificantly in brightness. However, when such encoded SDR and HDRinput video are equalized in accordance with a typical embodiment of theinvention (e.g., with the code values indicative of the HDR input videobeing passed through the equalizer unchanged, and the code valuesindicative of the SDR input video being mapped to code values in asubrange from 0 through T of the full range of the HDR video encodingscheme and then undergoing a second stage of mapping to expand theirdynamic range while keeping the mean of the equalized SDR content'sluminance at least substantially equal to that of the original SDRcontent and windowing the equalized SDR content and equalized HDRcontent to a common anchor point), and such equalized video is thenemployed to display a sequence of images, the average brightness of thedisplayed images will not fluctuate significantly.

In some implementations of FIG. 2, all the input video content (to bedelivered) is assumed to have the same white point (e.g., a white pointof D65). In other implementations of the inventive system and method,however, the white point of the input video is assumed to be variabledepending on the type of input video content to be equalized and how theinput video content is encoded, and the inventive system (or method) isimplemented to perform video equalization in accordance with theinvention in a manner that adjusts for such white point variation. Whenvideo content is encoded as a sequence of code words (e.g., with each ofthe code words having value in the range from 0 through 1) and suchencoded video is delivered to an end user and conventionally employed(without equalization in accordance with the invention) to display asequence of images having different white point (and/or color gamut),variation in the white point can also cause the displayed images tofluctuate significantly in brightness and/or variation in the colorgamut can cause the aesthetic appearance of the displayed images tofluctuate significantly. However, when SDR and HDR input video (havingvarying white point and/or color gamut) is equalized in accordance withan embodiment of the invention, and the equalized video is employed todisplay a sequence of images, the average brightness (determined by thedynamic range and white point of the equalized video) and aestheticappearance (determined by the color gamut of the equalized video) of thedisplayed images will not fluctuate significantly.

With reference again to FIG. 2, video equalization is implemented at twostages in the FIG. 2 system in a different manner at each stage.Specifically, within national broadcaster installation 31 the videocontent is equalized (in block 10) before the equalized content is timedivision multiplexed by switcher 5. In regional broadcaster installation33, the video content is equalized (in block 20) after time divisionmultiplexing of multiple streams in switcher 19. The pre-multiplexingimplementation (e.g., in block 10) requires all the input video contentto be mapped into a common dynamic range. This can have the disadvantageof requiring multiple mappers (e.g., where equalizer 10 implements adifferent mapper for each input video stream) and additional buffers tostore the data, but typically has the advantage of requiring lessanalysis (or no analysis) of the input video to be equalized. Thepost-multiplexing implementation (e.g., in block 20) has the advantagethat it typically requires only one mapper, but typically has thedisadvantage of requiring analysis of all the video content to beequalized (all the content in the time-division multiplexed stream to beequalized) or detection of metadata (provided with the video content tobe equalized) to control the equalization of the single video stream tobe equalized (e.g., the output of switcher 19 of FIG. 2).

With the post-multiplexing implementation of equalization (e.g., inblock 20), video content to be equalized can be analyzed (to determinethe type of equalization to be applied thereto) by a method includingone or more of the following steps:

-   -   detecting a characteristic of the video content (e.g.,        determining whether it is Rec. 709 RGB video, or whether it has        a white point of D65, or detecting its maximum luminance (e.g.,        determining that its maximum luminance or intensity is 100        nits), and assuming that the detected characteristic implies        that the video has a specific dynamic range (and optionally also        a specific white point and/or gamut);    -   detecting the presence of metadata provided with the video        content (e.g., assuming that the video content is HDR content in        response to detecting the presence of metadata); or    -   determining from metadata provided with (e.g., appended to) the        video content the type of equalization to be applied to the        video content.

Some examples of methods for analyzing video content to be equalized (todetermine the type of equalization to be performed thereto) are:

-   -   monitoring the mean luminance of an image (or each image)        determined by the content;    -   monitoring the geometric mean luminance of an image (or each        image) determined by the content    -   monitoring the logarithmic geometric mean luminance of an image        (or each image) determined by the content; and    -   monitoring peak brightness.

Different embodiments of the invention accomplish adaptation(equalization) of video content in different ways. Typically, the goalis to adapt content having lesser dynamic range (e.g., SDR contenthaving relatively low dynamic range) to content having greater dynamicrange content (e.g., VDR content). However, the adaptation is in theopposite direction (from relatively high dynamic range to relatively lowdynamic range) in alternative embodiments (e.g., so that SDR contentinput to the equalizer passes through the equalizer unchanged and thedynamic range of HDR content input to the equalizer is decreased).

In some embodiments in which a video equalizer (e.g., equalizer 10 or20) is configured to receive both video (e.g., encoded video) havingrelatively low dynamic range (low DR content) and video (e.g., encodedvideo) having relatively high dynamic range (high DR content), one orboth of the low DR content and high DR content is live content that hasbeen generated using at least one camera. For example, in the broadcastinstallation shown in FIG. 4, low DR content and high DR content (to beequalized by video equalizer 10) is generated by a mix of SDR and HDR(e.g., VDR) enabled cameras 40, 41, and 42. In some implementations ofFIG. 4, the video to be equalized by equalizer 10 also includes storedvideo (e.g., video stored in memory 43 of FIG. 4 for video replay use).FIG. 4 is a block diagram of a variation on broadcast installation 31 ofFIG. 2, in which equalizer 10 is coupled to receive input streams fromcameras 40, 41, and 42 (and optionally also memory 43) rather than videoinput streams 4A, 4B, and 4C. Metadata from at least one of cameras 40,41, and 42 (e.g., a camera implementing Cooke/I-technology), which maybe indicative of lens type, focus, Iris, F-stop, focal length, shutter,and/or the captured brightness of the content, can be provided to videoequalizer 10 and analyzed (by equalizer 10) to drive the equalization.The video equalization can be performed across the cameras only or intothe encoding space.

By including an embodiment of the inventive video equalizer as a stagein a display (e.g., display 50 of FIG. 5 or display 60 of FIG. 6), onecan ensure that the gamut/Dynamic range can be managed so that to theviewer there is no or very little variance in color or brightness of thedisplay (when a sequence of video streams from different sources aredisplayed).

FIG. 5 is a block diagram of a system including video stream source 46,delivery subsystem 2, and display system 50. Source 46 is configured toassert to subsystem 2 an encoded (typically, MPEG encoded) video stream.The video stream is a sequence of video segments, time-divisionmultiplexed together, and typically including video segments ofdifferent types (e.g., SDR segments time-division multiplexed with HDRsegments). The video stream typically includes metadata indicative ofthe type of video equalization to be applied to the video content ofeach of the segments (e.g., the metadata may be indicative of the typeof video content of each of the segments). The metadata may be includedin a header of each of the segments. Source 46 may (but need not) be animplementation of broadcast installation 33 of FIG. 2 that is configuredto include metadata of the noted type in the video stream. The videostream output from source 46 may be stored by subsystem 2 (e.g., in theform of a DVD or Blu ray disc), or transmitted by subsystem 2 (which mayimplement a transmission link or network), or may be both stored andtransmitted by subsystem 2.

Display system 50 includes codec 51 which is configured to decode theencoded (typically, MPEG encoded) video stream delivered to system 50 bysubsystem 2, and to assert the decoded video content (typically a streamof code values indicative of RBG or Yuv video, or other tri-stimulusdata) to latency buffer 53 and to video equalization management stage(equalization manager) 55.

Equalization manager 55 (sometimes referred to as a video equalizationmanagement block or “VEB”) is configured to provide image analysis ofthe content by decoding metadata (output from codec 51) and/or analyzingthe decoded content itself (also output from codec 51). The result ofthe analysis enables equalization manager 55 to assert control data(e.g., mapping parameters) to color management block 57 to enable block57 to perform video equalization in accordance with the invention on thedecoded video stream read out from buffer 53 (to generate an equalizedvideo stream). Block 57 typically also performs other (conventional)processing on the equalized video stream to generate display data fordriving HDR display 59, to cause display 59 to display a sequence ofimages determined by the display data. Display 59 is configured todisplay HDR video, and thus is configured to display a sequence ofimages in response to an equalized video stream comprising equalized SDRsegments (equalized by mapping input SDR code values to code values ofan HDR encoding scheme in accordance with an embodiment of the inventivemethod) time-division multiplexed with HDR segments (which are typicallyunchanged during equalization in accordance with the implementedembodiment of the inventive method).

During performance of video equalization in accordance with theinvention, block 57 typically:

identifies SDR content and HDR content in the video stream read frombuffer 53 (e.g., in response to identification of corresponding metadatafrom codec 51, or in response to identification of control data fromblock 55 determined from such metadata); and

equalizes the SDR and HDR content (e.g., maps the code values of the SDRcontent to code values of the HDR encoding scheme, and passes throughunchanged the code values of the HDR content, in accordance with anembodiment of the inventive equalization method. For example, theequalization of SDR content can be performed when SDR video commercialsare detected in a stream of HDR video segments). Block 57 can alsoenable a mode of operation of display 50 which phases transitions to orfrom SDR content and HDR content to prevent huge changes in the visualpresentation during such transitions.

Block 55 can guide video equalization (performed by block 57) in eitherof two methods:

generating mapping parameters for color management block 57 (e.g., usingassumed prediction parameters for identified SDR content, e.g., byassuming that identified SDR content is REC709 video having 100 nitdynamic range and a white point of D65); or

creating metadata from analysis of video content from codec 51, andasserting the metadata to color management block 57 to allow block 57 togenerate required mapping parameters and perform all mapping required toperform equalization on the content from buffer 53. Alternatively (e.g.,in another operating mode of display system 60), such metadata isasserted directly from codec 51 to block 57.

Latency buffer 53 is configured to capture the decoded video data fromcodec 51, and accounts for the latency within block 55.

Color Management block 57 is configured to perform equalization,typically including by performing dynamic range expansion (orcompression) using mapping algorithms of the type described herein(e.g., with reference to equalizers 10 and 20 of FIG. 2). Theequalization is guided by parameters driven out of block 55 (or asserteddirectly to block 57 from codec 51). Blocks 55 and 57, consideredtogether, implement a video equalizer.

FIG. 6 is a block diagram of a display system (60) which implementsanother embodiment of the inventive video equalizer. All elements ofFIG. 6 which are identical to corresponding elements of FIG. 5 areidentically numbered in FIGS. 5 and 6.

Architecturally, display system 60 is in alternative implementation ofdisplay system 50 of FIG. 5 display, in which the equalization manager(video equalization management block 65) is configured to be inline ofthe video path and to normalize SDR content to the HDR range (innormalization stage 68) and to drive out (to color management block 67)HDR video content and normalized SDR video content for equalization.Blocks 65 and 67 of display system 60, considered together, implement avideo equalizer. In response to the equalized video generated in block67, block 67 generates (and asserts to HDR display 59) display datadisplayable by HDR display 59. Equalization in block 67 is guided bycontrol data generated in block 64 and asserted via multiplexer 66 toblock 67, or by metadata (metadata from codec 51, or metadata newlygenerated in block 64) asserted via multiplexer 66 to block 67. Thelatency of multiplexer 66 accounts for the time required for videoanalysis and normalization within elements 64 and 68.

Display system 60 includes codec 51 which is configured to decode theencoded (typically, MPEG encoded) video stream delivered to system 50 bysubsystem 2, and to assert the decoded video content (typically a streamof code values indicative of RBG or Yuv video, or other tri-stimulusdata) to block 65, and optionally also to assert to block 65 metadata(indicative of the type of video equalization to be applied to the videocontent of each segment of the decoded video stream) extracted from theencoded video delivered by subsystem 2.

Video/metadata analysis stage 64 of block 65 is configured to passthrough the decoded video from codec 51 to normalization stage 68. Stage68 is configured to normalize SDR content of the video to the HDR rangeand to drive out (to color management block 67 for equalization) anormalized video stream comprising segments of HDR video content andnormalized SDR video content. Block 67 is configured to generatedequalized video in response to the normalized stream from stage 68 and,in response to the equalized video, to generate (and assert to HDRdisplay 59) display data displayable by HDR display 59.

Video/metadata analysis stage 64 is also configured to provide imageanalysis of the decoded video content from codec 51 by analyzing thedecoded content. As a result of the analysis, stage 64 asserts controldata (e.g., mapping parameters) and/or metadata to color managementblock 67 (via multiplexer 66) to enable block 67 to perform videoequalization in accordance with the invention on the normalized, decodedvideo stream from stage 68 (to enable block 57 to generate an equalizedvideo stream). Stage 64 may assert to element 66 a control bit (or othercontrol signal) which selects the data (e.g., metadata from codec 51 orcontrol data (or metadata) generated in stage 64) asserted at the outputof element 66 to block 67. Stage 64 also asserts control data and/ormetadata (indicative of whether the current segment of the video streamis SDR or HDR content) to normalization stage 68, to enable stage 68 tonormalize the SDR content to the HDR range.

Optionally, metadata indicative of the type of video in each of thesegments of the stream output from codec 51 (and thus the videoequalization to be performed on each of the segments) is provided tomultiplexer 66 from codec 51, or is generated by stage 64 by analyzingthe decoded video from codec 51 (and asserted by stage 64 to multiplexer66). Multiplexer 66 asserts to block 67 the control data and/or metadatagenerated by stage 64, or the metadata from codec 51 that coincides withthe video source.

As well as performing video equalization in accordance with theinvention on the video stream from stage 68 (to generate an equalizedvideo stream), color management block 67 typically also performs other(conventional) processing on the equalized video stream to generatedisplay data for driving HDR display 59, to cause display 59 to displaya sequence of images determined by the display data. Display 59 isconfigured to display HDR video, and thus is configured to display asequence of images in response to an equalized video stream comprisingequalized SDR segments (equalized by mapping input SDR code values tocode values of an HDR encoding scheme in accordance with an embodimentof the inventive method) time-division multiplexed with HDR segments(which are typically unchanged during equalization in accordance withthe implemented embodiment of the inventive method).

Other aspects of the invention are a processor (e.g., a FPGA, an ASIC,or a system on a chip (SOC)) configured to perform any embodiment of theinventive encoding method (e.g., equalizer 10 of FIG. 2 or FIG. 4,equalizer 20 of FIG. 2, elements 55 and 57 of FIG. 5, or elements 65 and67 of FIG. 6, implemented as a general or special purpose processor),and a system including such a processor and a subsystem for generatinginput video (to be equalized in accordance with the invention), andoptionally also one or both of a delivery subsystem configured to storeand/or transmit an encoded representation of equalized video generatedin accordance with the invention, and a display subsystem for displayingequalized video generated in accordance with the invention. Embodimentsof the inventive processor are (or include) a general or special purposeprocessor (e.g., a digital signal processor or microprocessorimplemented as an integrated circuit (chip) or chip set) which isprogrammed with software (or firmware) and/or otherwise configured toperform an embodiment of the inventive method. Another aspect of theinvention is a computer readable medium (e.g., a disc) which stores codefor programming a processor to implement any embodiment of the inventivemethod.

The present invention may suitably comprise, consist of, or consistessentially of, any of the steps and elements (the various parts andfeatures of the invention) and their equivalents as described herein.Some embodiments of the present invention illustratively disclosedherein are practiced in the absence of one or more of the steps andelements described herein, whether or not this is specifically disclosedherein. Numerous modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed is:
 1. A method of video equalization, said methodcomprising: receiving input video including a first video stream havinga first dynamic range and second video stream having a second dynamicrange different than said first dynamic range; defining a common anchorpoint associated with said input video and equalized video to begenerated; performing equalization on said input video based on saidcommon anchor point to generate said equalized video, said equalizedvideo defining a sequence of images having dynamic range that isconstant to a predetermined degree; and wherein said sequence of imagesincludes at least one image associated with said first video stream andat least one image associated with said second video stream; and imagesof said sequence of images have substantially the same average luminanceas associated images of said input video; and wherein said first dynamicrange is larger than said second dynamic range; said first video streamis encoded with code values having a full range; and said step ofperforming equalization on said input video comprises mapping codevalues of said second video stream to code values in a subrange of saidfull range of code values associated with said first video stream suchthat said mapping expands said second dynamic range.
 2. The method ofclaim 1, further comprising performing equalization on said input videosuch that said sequence of images of said equalized video has at leastone of color gamut and white point that is constant to a predetermineddegree.
 3. The method of claim 1, wherein said sequence of images ofsaid equalized video has dynamic range that is substantially constant.4. The method of claim 3, further comprising performing equalization onsaid input video such that said sequence of images of said equalizedvideo has at least one of color gamut and white point that issubstantially constant.
 5. The method of claim 1, wherein said commonanchor point comprises a predetermined gray level.
 6. The method ofclaim 5, wherein said predetermined gray level comprises a 20% graylevel.
 7. The method of claim 1, wherein said common anchor pointcomprises the log mean of luminance of said input video.
 8. The methodof claim 1, wherein said common anchor point comprises one of theaverage, the geometric mean, and the log of the geometric mean ofluminance of said input video.
 9. The method of claim 1, wherein: saidinput video comprises an input video stream having a sequence of inputvideo segments; said step of performing equalization includes performingequalization on said input video segments to generate a sequence ofequalized video segments; video of at least one of said input videosegments is adjusted such that a sequence of images defined by saidsequence of equalized video segments has substantially-constant dynamicrange; and images defined by said input video segments do not havesubstantially-constant dynamic range.
 10. The method of claim 9, furthercomprising determining said equalization to be performed on each of saidinput video segments by analyzing said input video stream.
 11. Themethod of claim 9, further comprising determining said equalization tobe performed on each of said input video segments based on metadataprovided with said input video stream.
 12. The method of claim 9,further comprising generating said input video stream by decoding anencoded video stream delivered by a video delivery system.
 13. Themethod of claim 1, further comprising: performing equalization on videosegments associated with a plurality of video streams of said inputvideo to generate equalized video segments; and combining said equalizedvideo segments into a combined video stream; and wherein saidequalization adjusts video of at least one of said video segments suchthat images defined by said combined video stream havesubstantially-constant dynamic range; and said images defined by saidcombined video stream are associated with different ones of saidplurality of video streams of said input video having different dynamicranges.
 14. The method of claim 1, wherein said dynamic range of saidsequence of images of said equalized video comprises said first dynamicrange.
 15. The method of claim 14, wherein: said first dynamic range isgreater than said second dynamic range; and said step of performingequalization comprises expanding said second dynamic range.
 16. Adisplay system comprising: a video equalizer coupled and configured toreceive an input video stream and to perform equalization on said inputvideo stream to generate an equalized video stream, said input videostream comprising a plurality of video segments including at least onevideo segment having a first dynamic range and at least one videosegment having a second dynamic range different than said first dynamicrange; and a subsystem coupled to said video equalizer and configured todisplay images in response to said equalized video stream; and whereinsaid equalized video stream defines a sequence of images including atleast one image associated with at least one of said video segmentshaving said first dynamic range and at least one image associated withat least one of said video segments having said second dynamic range,said sequence of images having dynamic range that is constant to apredetermined degree; said video equalizer is further configured toperform said equalization based on a common anchor point associated withsaid input video stream and said equalized video stream; and imagesdefined by said equalized video stream have at least substantially thesame average luminance as associated images defined by said input videostream; and wherein said video equalizer is configured to determine saidequalization to be performed on each of said video segments of saidinput video stream by analyzing said input video stream; and performsaid determined equalization for each of said video segments such thatsaid equalized video stream includes a sequence of equalized videosegments.
 17. The display system of claim 16, further comprising adecoding stage configured to receive an encoded video stream, generatesaid input video stream by decoding said encoded video stream, andprovide said input video stream to said video equalizer.
 18. The displaysystem of claim 17, wherein: said decoding stage is further configuredto provide metadata to said video equalizer with said input videostream; and said video equalizer is further configured to determine saidequalization to be performed on each of said video segments of saidinput video stream based on said metadata and perform said determinedequalization for each of said video segments such that said equalizedvideo stream includes a sequence of equalized video segments.
 19. Thedisplay system of claim 16, wherein said video equalizer is furtherconfigured to perform said equalization such that said sequence ofimages defined by said equalized video stream has at least one of colorgamut and white point that is constant to a predetermined degree.
 20. Amethod of video equalization, said method comprising: receiving inputvideo including a first portion having a first dynamic range and secondportion having a second dynamic range different than said first dynamicrange; defining a common anchor point associated with said input videoand equalized video to be generated; performing equalization on saidinput video based on said common anchor point to generate said equalizedvideo, said equalized video defining a sequence of images having dynamicrange that is constant to a predetermined degree; and wherein saidsequence of images includes at least one image associated with saidfirst portion of said input video and at least one image associated withsaid second portion of said input video; images of said sequence ofimages have substantially the same average luminance as associatedimages of said input video; said input video comprises an input videostream having a sequence of input video segments; said step ofperforming equalization includes performing equalization on said inputvideo segments to generate a sequence of equalized video segments; videoof at least one of said input video segments is adjusted such that asequence of images defined by said sequence of equalized video segmentshas substantially-constant dynamic range; and images defined by saidinput video segments do not have substantially-constant dynamic range.21. The method of claim 20, further comprising determining saidequalization to be performed on each of said input video segments byanalyzing said input video stream.
 22. The method of claim 20, furthercomprising determining said equalization to be performed on each of saidinput video segments based on metadata provided with said input videostream.
 23. The method of claim 20, further comprising generating saidinput video stream by decoding an encoded video stream delivered by avideo delivery system.
 24. A method of video equalization, said methodcomprising: receiving input video including a first video stream havinga first dynamic range and second video stream having a second dynamicrange different than said first dynamic range; defining a common anchorpoint associated with said input video and equalized video to begenerated; performing equalization on said input video based on saidcommon anchor point to generate said equalized video, said equalizedvideo defining a sequence of images having dynamic range that isconstant to a predetermined degree; and wherein said sequence of imagesincludes at least one image associated with said first video stream andat least one image associated with said second video stream; images ofsaid sequence of images have substantially the same average luminance asassociated images of said input video; and said step of performingequalization includes performing equalization on video segmentsassociated with said first video stream and said second video stream togenerate equalized video segments and combining said equalized videosegments into a combined video stream; said equalization adjusts videoof at least one of said video segments such that images defined by saidcombined video stream have substantially-constant dynamic range; andsaid images defined by said combined video stream are associated withdifferent ones of said first and second video streams of said inputvideo having different dynamic ranges.
 25. A method of videoequalization, said method comprising: receiving input video including afirst video stream having a first dynamic range and second video streamhaving a second dynamic range different than said first dynamic range;defining a common anchor point associated with said input video andequalized video to be generated; performing equalization on said inputvideo based on said common anchor point to generate said equalizedvideo, said equalized video defining a sequence of images having dynamicrange that is constant to a predetermined degree; and wherein saidsequence of images includes at least one image associated with saidfirst video stream and at least one image associated with said secondvideo stream; and images of said sequence of images have substantiallythe same average luminance as associated images of said input video;said dynamic range of said sequence of images of said equalized videocomprises said first dynamic range; and said first dynamic range isgreater than said second dynamic range, and said step of performingequalization comprises expanding said second dynamic range; or saidfirst dynamic range is less than said second dynamic range, and saidstep of performing equalization comprises compressing said seconddynamic range.
 26. The method of claim 25, wherein: said first dynamicrange is greater than said second dynamic range; and said step ofperforming equalization comprises expanding said second dynamic range.27. The method of claim 25, wherein: said first dynamic range is lessthan said second dynamic range; and said step of performing equalizationcomprises compressing said second dynamic range.